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Background:

Imagine there is a planet in a solar system which has an atmosphere (let's say it is similar to our own atmosphere, but it doesn't have to be) and a very technologically advanced species lives on its surface. The star in the solar system will explode in the next few hundred years, destroying the planet. The species die if they get too far away from their planet, so escaping in generation ships isn't an option.

The species who live on the planet have a way to move the entire planet out into deep space using a magic system, but they don't have a way to maintain their atmosphere once it is away from their star and they become a rogue planet.

The Question:

Assuming that there aren't any technological restrictions in place, how could the atmosphere be maintained once in deep space? The magic system in place can be used to explain away some minor handwavery, but the solution should be mainly technological.

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  • $\begingroup$ Are you trying to retain the atmosphere and surface ecosystem as-is? Or can the whole thing be radically remodelled? $\endgroup$ – Starfish Prime Mar 2 at 12:26
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    $\begingroup$ Can you explain why the atmosphere won't be retained in deep space? What would make it escape? Their main problem will be extreme cold without a sun to keep them warm. $\endgroup$ – chasly - supports Monica Mar 2 at 12:29
  • $\begingroup$ @StarfishPrime, There can be some remodelling, but the general ecosystem on the surface and the atmospheric composition should remain largely the same as before. $\endgroup$ – Brad0440 Mar 2 at 12:39
  • $\begingroup$ @chasly-supportsMonica, I guess I'm less worried about it escaping (although from what I can gather that is a possibility), and more looking for a way to maintain it as is without changing too much. If you'd just need to generate enough heat and there aren't any other worries then that's great! $\endgroup$ – Brad0440 Mar 2 at 12:41
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    $\begingroup$ recommended reading: en.m.wikipedia.org/wiki/A_Pail_of_Air $\endgroup$ – ths Mar 3 at 0:48
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The colder the atmosphere, the lower the chance that it escapes into space, because the fraction of molecules exceeding the escape velocity will be lower.

Therefore the only worry of your species is to supply the atmosphere with enough heat to prevent it from condensing.

Maybe, if they are into energy saving, they could cover the whole planet with a thermal insulating shell at few kilometers of height, which would limit the heat dispersion toward space and, since it's there, also prevent gases from escaping. Not having a star to be dependent on for the energy supply makes it less problematic.

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    $\begingroup$ Doomed planet? Domed planet! $\endgroup$ – Willk Mar 2 at 14:39
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Being in deep space would not, of itself, cause the atmosphere to disappear.

They wouldn't have the heat from a Sun to warm the atmosphere. If they don't come up with some alternate heat source, the temperature of the atmosphere will plummet. Chemicals in the atmosphere will turn to liquids or solids and condense out.

A planet generates some heat: radioactive decay of elements in the crust, for example. I don't know how much heat this generates on Earth never mind on your hypothetical planet. My guess is not enough to make much difference, maybe keep you a few degrees above absolute zero. I'll gladly yield on this point to someone with actual information. (As I always say, speculating wildly is so much easier than doing research.)

Presumably the aliens are going to do SOMETHING to produce heat to keep themselves alive. Do they have the ability to produce enough heat to keep the whole planet warm? Or just enough to heat a few small shelters?

Other than producing enough heat to keep the temperature of the atmosphere high enough that everything doesn't condense out, I don't know what you could do. While, theoretically you could increase the atmospheric pressure, but how are you going to do that?

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